Abstract
The biosynthesis of molybdenum cofactor for redox enzymes is carried out by multiple enzymes in bacteria including MobA and MobB. MobA is known to catalyze the attachment of GMP to molybdopterin to form molybdopterin guanine dinucleotide. MobB is a GTP binding protein that enhances the activity of MobA by forming the MobA:MobB complex. However, the mechanism of activity enhancement by MobB is not well understood. The structure of Bacillus subtilis MobB was determined to 2.4 Å resolution and it showed an elongated homodimer with an extended β-sheet. Bound sulfate ions were observed in the Walker A motifs, indicating a possible phosphate-binding site for GTP molecules. The binding assay showed that the affinity between B. subtilis MobA and MobB increased in the presence of GTP, suggesting a possible role of MobB as an enhancer of MobA activity.
Highlights
Molybdenum is an essential trace element required in diverse redox reactions in bacteria and eukaryotes [1]
MobB increased in the presence of guanosine triphosphate (GTP), suggesting a possible role of MobB as an enhancer of Keywords: molybdenum cofactor; MobB; Walker A motif; Bacillus subtilis; crystallography
molybdenum cofactor (Moco) biosynthesis is carried out by a conserved pathway with multiple steps (Figure 1): first, the formation of cyclic pyranopterin monophosphate from guanosine triphosphate (GTP) [3], followed by the insertion of two sulfur atoms to form
Summary
Molybdenum is an essential trace element required in diverse redox reactions in bacteria and eukaryotes [1]. Two MGDs can be ligated to a single molybdenum atom, forming the bis-MGD cofactor, a reaction catalyzed by MobA and MobB proteins [13]. MobA is crucial for this reaction and MobB, a GTP-binding protein with weak intrinsic GTPase activity [14], enhances the function of MobA by forming the MobA:MobB complex as shown by an increased activity of nitrate reductase that requires bis-MGD as a cofactor [11]. Our crystal structure of B. subtilis MobB showed that it formed an elongated homodimer. MobB, which showed that these two proteins interacted more strongly in the presence of GTP in agreement with the suggested MobA:MobB complex model. Biosynthesisofofmolybdenum molybdenum cofactor further modifications to MCD bis-MGD in bacteria. MobA and MobB catalyze the conversion of Moco to bis-MGD
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